It was booting to spinning dots on a black screen, now it boots to an error message with an Advanced Options button to get to the recovery environment. Does the button work? Or do you get dots? It seems better, but not good enough. I don't think it worthwhile to set it back the way it was. It was trying to boot directly to the recovery environment instead of to Windows 10.
(1) Well, I see you reverted your Registry. Did that work?
(2) No, I don't think putting BIOS into UEFI mode will be helpful, because you've got a Legacy install. But try it, if you want.